The principles of the present invention are applicable to industrial fastener driving tools of the type utilized to drive staples, nails, or other fastening means. While not intended to be so limited, the present invention will, for purposes of an exemplary showing, describe the invention in its application to an industrial staple driving tool.
In the manufacture of industrial staplers and nailers, it is common practice to provide a guide body and an associated latchable gate at the lower front nose portion of the tool. The guide body and gate (in closed position) define a drive track for the tool driver and fastener elements. The purpose of the gate is to provide access to the drive track in the event of the jamming of a fastener in the drive track.
Prior art workers have devised numerous types of gate and gate latch assemblies. Examples of such structures are taught in U.S. Pat. Nos. 3,273,777; 3,905,535; and 4,139,137.
The prior art gate and latch assemblies, of which the above mentioned patents are exemplary only, have been characterized by certain deficiencies. Force is applied to the gate latch each time a fastener is driven, because the door is a part of the drive track. This has frequently caused excessive wear of the latch mechanism. In many prior art structures, the forces required to latch and unlatch the gate are high. When the tool is jammed, as much as a 1.5 ton load may be applied to the gate. The force required to unlatch the gate frequently becomes so high, when a fastener is jammed in the drive track, that a hammer or other tool is required to unlatch the front gate.
The structure of the present invention was developed to overcome these problems and to provide a positive, easy-to-operate latch which will allow clearing of jammed fasteners with minimal effort. The structure of the present invention utilizes a three-point over-center latch mechanism attached to a moving wedge, mounted on the gate. The wedge is moved into and out of engagement with locking blocks mounted on the tool guide body. The shifting of the wedge is accomplished by operating the latch lever through an angle of about 120.degree..
In the structure of the present invention, the front gate is rigidly held shut during the driving of a fastener. The load bearing surfaces of the latch mechanism have been enlarged to prevent deformation and wear. The load bearing surfaces of the mating parts of the wedge and the locking blocks transmit almost all of the loads from the front gate, through the wedge into the locking blocks and thus into the guide body. The use of a wedge for this purpose provides relatively large load bearing surfaces, thus reducing the unit stress to a minimum. The wedge has a taper in the neighborhood of 16.degree. which is a non-locking taper so that the latch can be readily opened by hand. The taper also allows for releasing the load with a minimum of sliding contact movement of the mating parts, thus reducing wear on the parts. The over-center latch mechanism incorporates an adjusting screw. This allows all parts to be manufactured using maximum tolerances. Such adjustment can be made without the use of tools.